Abstract - The aim of the first experiment conducted was to further
characterise HPA axis functionality in male mule ducks during the
force-feeding period, by measuring corticosterone levels (Exp. 1). The
objectives of the two other experiments were to investigate the impact of
different rearing conditions on stress response (Exp. 2) and behaviour
patterns (Exp. 3) in male mule ducks. The rearing conditions examined
comprised individual (Exps. 1-3) and collective battery cages (Exps. 2, 3), as well as collective floor pens (Exps. 2, 3). The ducks were
then fed (Exps. 1-3) by force-feeding for foie gras production or
ad libitum (Exp. 1). The highest levels of corticosterone (up to 100 ngmL-1) were measured after initial capture and handling in a large
collective rearing pen, transfer to a different environment, initial
placement in a net for 10 min and injection of 5 gkg-1 BW
of 1-24 ACTH agonist. Both force-fed and non-force fed male mule ducks
responded to a first physical constraint in a net by a large increase in
corticosterone levels. Their HPA axis was therefore functional although the
effect quickly vanished, which was interpreted as an indication that
habituation took place. Most often, corticosterone levels measured before
and after force-feeding during the force-feeding period did not differ
significantly (P > 0.05) when the ducks were raised in individual cages,
even on the first occurrence. A significant increase in corticosterone
levels was observed after the first force-fed meal for both groups of ducks
raised collectively, i.e. in cages or floor pens, when the practice involved
capture and handling. Following the injection of 0.625 and 5 gkg-1 BW doses of 1-24 ACTH, cortico-adrenal responses were
significantly (P < 0.05) higher and lower for ducks raised in collective
floor pens compared to those raised in individual cages, respectively. This
hypersensitivity and lower maximal capacity may result from a chronic
stressful state related to repeated acute stress (i.e. capture and handling
twice daily). Ducks raised in cages (individual or collective) spent more
time standing (less lying) and less time inactive i.e. expressing passive
behaviour patterns, which suggest that they were not presenting signs of
passive coping or learned helplessness. Behaviour observations did not
provide any indication of stereotyped behaviour. From these results, it
could have been concluded that placement in individual battery cages the limited period of force-feeding are not detrimental in terms of welfare.
However, they
cannot achieve full wing stretching or express a full range of
social behaviours as required by the European Council recommendation (Scientific Committee on Animal Health and Animal Welfare, Welfare
aspects of the production of foie gras in ducks and geese, CEC,
DGXXIV/B3/AW/R06, 1998, 94 p.). They may also have more difficulty in thermoregulating as indicated by the
fact that they had higher frequencies of both panting and watering.
In terms of welfare, since signs of acute and possibly chronic stress were
observed when the force-feeding procedure involved capture and handling,
there is a need to set up new models of collective cages and better define
the optimal group size and density to be used in future rearing conditions.